Most pilot valves are mounted on the main relief valve with brackets and fluid pressure is transmitted to the pilot valve by suitable tubing. Pilot operated relief valves having tubing connections between the main valve body and the pilot valve body are subject to possible leakage and a high manufacturing cost.
In some instances, such as shown in U.S. Pat. Nos. 4,172,466 and 5,842,501, the pilot valve has been connected directly to the main valve body without the use of brackets and separate tubing lines between the pilot valve body and the main relief valve body. However, the pilot valve body is connected to the main valve body along planar or flat surfaces and possible leaks may occur along such faces or surfaces.
In some instances in which a plate-type main valve member having a diaphragm actuator is provided, a pilot valve has been mounted on a cap on the main valve body over the main diaphragm chamber with the plate-type main valve member connected directly to the diaphragm actuator.
It is desired that a pilot operated relief valve be provided in which the main valve member comprises a piston with a pilot valve axially mounted on a cap for the main valve body adjacent a dome chamber over the piston.